This application claims priority of German patent application number 19938377.4, filed Aug. 6, 1999.
The invention concerns a stent, and, in particular a coronary stent for implantation in the region of vessel branchingand having a tubular casing with a proximal end and a distal end.
A stent is an intraluminal support element. Such a support element serves to support the wall of a generally constricted vessel in the human or animal body in order to hold the vessel in a dilated position. Stents of that kind are frequently used, as so-called coronary stents, in the region of constricted coronary blood vessels.
In that respect, known stents generally consist of a tubular casing with a proximal end and a distal end, which is moved in a non-expanded condition to the location to be dilated in the vessel. When it is in the desired position the casing is suitably expanded, radially, to a diameter at which the vessel wall therearound is dilated to the desired diameter. Thereafter, the stent of its own accord remains in that condition in order to hold the vessel in a permanently dilated state.
It is frequently necessary for the stent to be implanted in the region of vessel branchings. Stents are known for that purpose, in such stents, in the implanted condition, the proximal end is arranged in proximal relationship with the vessel branching and the distal end is arranged in distal relationship with the vessel branching. Such stents also have at least one branching portion which is arranged at the periphery of the casing and which is disposed in the implanted condition in the region of the vessel branching. Upon implantation, that branching portion is generally deformed in such a way that it opens a passage into the branching-off branch of the vessel.
Such a stent is known, for example, from European patent application No. EP 0 904 745 A2. In that stent, to open the passage into the branching-off branch of the vessel, one or more first support elements, which are in mutually adjoining relationship in the peripheral direction of the stent and which extend from a first direction, in this case the direction of one end of the casing into the branching portion, are pivoted substantially radially by plastic deformation out of the peripheral surface of the casing into the branching-off branch of the vessel.
However, the problem which arises in such a stent design is that the vessel transition of the branching configuration is inadequately supported. The vessel transition is on the one hand a highly sensitive region of the vessel, which is subjected to a particular loading when a stent is implanted only in one branch of the vessel. On the other hand, maintenance of its natural geometry is an aspect of significance from points of view relating to flow dynamics therein, as it is only in that way that the normal circulation can be restored, and, for example, the only way formation of deposits due to detrimental flow conditions can be avoided.
Admittedly, the first support element of the known stent already permits a certain amount of support for the vessel transition. That, however, is only at one side and therefore under some circumstances it results in an unwanted unnatural deformation and loading of the vessel transition.
Therefore the object of the present invention is to provide a start of the kind set forth in the opening part of this specification, for providing improved support for the vessel transition in the region of a vessel branching.
The present invention is directed to a stent of the kind set forth in the opening part of this specification, where the branching portion includes at least one second support element which is provided for supporting the vessel transition, and which can be pivoted substantially radially out of the peripheral surface, and which extends from a second direction different from the first direction into the branching portion.
The invention embraces the technical teaching that an improved supporting action for the vessel transition is achieved if the branching portion includes at least one second support element which is provided for supporting the vessel transition, and which can be pivoted substantially radially out of the peripheral surface, and which extends into the branching portion from a direction which is in a substantially opposite relationship to the first. In this arrangement, the two support elements can be pivoted into the branching-off branch of the vessel in the manner of a saloon door, and thereby support the vessel transition from two oppositely disposed points. This ensures that the loadings are more uniformly applied to the delicate vessel transition, as occur for example precisely in the case of movements of the vessel transversely with respect to the plane of the branching, with such movements being strong movements in the region of the coronary vessels.
In one embodiment, the first direction may entail any desired direction. Thus it is possible for example for the first direction to extend from the distal end of the stent parallel to the longitudinal axis thereof. It is, however, also possible for the first direction to extend in a peripheral direction of the stent.
In another embodiment, there is provided at least one third support element which is arranged adjacent to the first or second support element transversely with respect to the first direction. The support portions can be uniformly distributed and for example can extend into the branching portion from directions which are mutually displaced through 120xc2x0 relative to each other. Such an arrangement ensures an even more uniform supporting effect. This supporting effect can also be additionally improved if the stent has a fourth support element, arranged transversely in relation to the first direction, in adjacent relationship with the first and second support elements. It will be appreciated, moreover, that it is also possible to provide firer respective support elements, which are arranged in adjacent relationship transversely with respect to the first direction.
In another embodiment, the first and second support elements can be arranged in such a way that in the initial condition they are in mutually adjoining relationship, transverse with respect to the first direction, that is to say they extend along each other over a given length Preferably, the second support element is arranged in substantial alignment with the first support element in the first direction- This permits simple positioning of the stent in the region of the vessel branching with a branching-off vessel branch of relatively small diameter. It is only necessary in that case for the two free ends of the support elements to be placed approximately in the center of the passage of the branching, which is possible, for example, by means of a guide wire which is passed through between the two ends.
In another embodiment of the stent according to the invention, the support elements are of an elongated configuration, whereby on the one hand simple deformation into the support position thereof is possible. On the other hand, support elements of this kind permit use thereof in vessel branchings of the most widely varying diameters in respect of the branching-off branch of the vessel. Thus, when the branching-off branch of the vessel is of relatively small diameter, only the free end region of the respective support element can be used to support the vessel transition, while when dealing with larger diameters, the support element possibly extends over its entire length into the branching-off branch of the vessel. Thus, the stent can provide a long support length and thus give a good supporting action.
In another embodiment of the invention, the support elements are formed by bar or web elements which extend substantially parallel to the first direction, and which are distinguished by particularly simple handling upon deformation thereof to assume their supporting position. In such an embodiment, the configuration of the bar or web elements in that arrangement is substantially in the manner of a hairpin, with the bend region forming the free end of the support element. This provides on the one hand a strong and stable support element, and on the other hand, with that arrangement, it is possible to adopt a particularly desirable configuration in which the limbs of the support element are connected to the casing in such a way that they move away from each other upon expansion of the stent. This results on the one hand in a stable support geometry, while on the other hand it results in support points for the wall of the vessel that are further away from each other and that are thus more uniformly distributed.
In another embodiment of the stent according to the invention, the support elements, which are in mutually adjoining relationship transverse to the first direction, are connected at their free end by way of at least one connecting element, thereby providing for support for the vessel transition over a relatively large surface area. Preferably, the connecting element is of an arcuate configuration so that, upon deformation of the support elements into their supporting position, lengthwise compensation can take place between the free ends.
In another embodiment of the invention, the support elements are of such a configuration and arrangement that in the implanted condition, with support elements which are pivoted radially out of the peripheral surface to support the vessel transition, the branching portion opens a passage in the peripheral surface, which passage is substantially adapted to the contour of the vessel transition. This ensures particularly uniform support for the transitional region.
In another embodiment of the stent according to the invention, which are particularly desirable because they are simple to fit in position, the stent has a number of branching portions. For positioning purposes, it is then generally sufficient to place any one of the branching portions in the region of the vessel branching.
In another embodiment, branching portions for passages of different dimensions are provided, which are suitable for use in the region of branching-off vessel branches of different diameters.
In another embodiment, at least a part of the branching portion is arranged in an annular region of the casing in the peripheral direction of the casing so that, for positioning a branching portion in the region of the vessel branching, the angular position of the stent only has to be changed about its longitudinal axis by a comparatively slight amount. In that respect, the amount is particularly slight if the branching portions are arranged in the annular region in an immediately mutually adjoining relationship.
The present invention further concerns a process for implanting a stent according to the invention, which is distinguished in that the support elements are pivoted radially out of the peripheral surface into the vessel branching after expansion of the casing in the manner of a saloon door by an actuating means which is moved to the branching portion. In that arrangement, the actuating means used is preferably a guide wire. Preferably in that arrangement the guide wire also serves for positioning the stent prior to expansion so that there is no need to provide or move to the stent a separate actuating means.
In another embodiment, to expand the stent use is made of a balloon catheter, which at its distal end has a balloon with a proximal chamber and a distal chamber spaced therefrom, between which chambers the guide wire forming the actuating means issues. That permits particularly fast and simple implantation of the stent.